Depositing heat-treated aluminum using ultrasonic consolidation

ABSTRACT

A system, method, and articles are disclosed with respect to depositing aluminum or alloys thereof, utilizing ultrasonic object consolidation. The method aspect of the invention comprises the steps of heat-treating an aluminum-based feedstock and ultrasonically consolidating the feedstock to a substrate to produce a part or a repair of a part, as might be required in an aerospace or aircraft structure. The feedstock may be solution heat-treated. This would include situations wherein the feedstock is solution heat treated off-line and maintained under controlled temperature conditions to prevent precipitation of solutes prior to the ultrasonic consolidation. Alternatively, the feedstock may be heat-treated on-line by passing it through a temperature- and/or atmosphere-controlled chamber prior to ultrasonic consolidation. The feedstock may be supported to minimize slumping due to creep. The feedstock may be T4, or may be aged, to T6, for example. The feedstock may be allowed to age naturally at room temperature, or a heat source may be used to artificially age the consolidated feedstock. The substrate may be aged or unaged. The source of the aluminum-based feedstock is in the form of tapes, sheets, wires, or droplets.

REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 60/629,421, filed Nov. 19, 2004, the entire content of which isincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to ultrasonic object consolidation and,in particular, to the deposition of heat-treated aluminum usingultrasonic consolidation without disturbing the properties of theunderlying material(s).

BACKGROUND OF THE INVENTION

Ultrasonic consolidation is an additive manufacturing technology used toproduce objects of any geometry from uniform, featureless feedstocks,such as tapes, sheets, wires, or droplets. There are a range of methodsfor accomplishing the metallurgical consolidation of the feedstocks viaultrasonic energy. These include, but are not limited to, spotconsolidation, continuous rotary consolidation, plate-typeconsolidation, and so forth.

My U.S. Pat. No. 6,519,500 is directed to a system and a method offabricating an object by adding material layers incrementally andconsolidating the layers through the use of ultrasonic vibrations andpressure. The layers are placed in position to shape the object by amaterial feeding unit. The raw material may be provided in variousforms, including flat sheets, segments of tape, strands of filament orsingle dots cut from a wire roll. The material may be metallic orplastic, and its composition may vary discontinuously or gradually fromone layer to the next, creating a region of functionally gradientmaterial. Plastic or metal matrix composite material feedstocksincorporating reinforcement materials of various compositions andgeometries may also be used.

If excess material is applied due to the feedstock geometry employed,such material may be removed after each layer is bonded, or at the endof the process; that is after sufficient material has been consolidatedto realize the final object. A variety of tools may be used for materialremoval, depending on composition and the target application, includingknives, drilling or milling machines, laser cutting beams, or ultrasoniccutting tools.

The consolidation is effected by ultrasonic welding equipment, whichincludes an ultrasonic generator, a transducer, a booster and a headunit, also called a horn or sonotrode. Ultrasonic vibrations aretransmitted through the sonotrode to the common contact surface betweentwo or more adjacent layers, which may include layers next to each otheron the same plane, and/or layers stacked on top of each other. Theorientation of the sonotrode is preferably adjusted so that thedirection of the ultrasonic vibrations is normal to the contact surfacewhen consolidating layers of plastic material, and parallel to thecontact surface when consolidating layers of metal.

The layers are fed sequentially and additively according to alayer-by-layer computer model description of the object, which isgenerated by a computer-aided design (CAD) system. The CAD system, whichholds the layered description of the object, interfaces with a numericalcontroller, which in turn controls one or more actuators. The actuatorsimpart motion in multiple directions, preferably three orthogonaldirections, so that each layer of material is accurately placed inposition and clamped under pressure. The actuators also guide the motionof the sonotrode, so that ultrasonic vibrations are transmitted in thedirection required through the common contact surfaces of the layersundergoing consolidation.

During the ultrasonic consolidation process, an ultrasonic power supplyis used to drive the sonotrode to a particular amplitude when applyingmaterial to a structure. The amount of power required to accomplish thisis constantly varying due to the constantly changing geometry of thestructure. This is prevalent in free-form fabrication applications, inwhich an arbitrary geometry is supplied to a manufacturing system, whichthem produces that arbitrary article from an essentially featurelessfeedstock, such as tape, wire or other tiny volumes of material.

SUMMARY OF THE INVENTION

This invention is directed to a system, method, and articles produced bydepositing aluminum or alloys thereof, utilizing ultrasonic objectconsolidation. The method aspect of the invention comprises the steps ofheat treating an aluminum-based feedstock and ultrasonicallyconsolidating the feedstock to a substrate to produce a part or a repairof a part, as might be required in an aerospace or aircraft structure.

The feedstock may be solution heat-treated. This would includesituations wherein the feedstock is solution heat treated off-line andmaintained under controlled temperature conditions to preventprecipitation of solutes prior to the ultrasonic consolidation.Alternatively, the feedstock may be heat-treated on-line by passing itthrough a temperature- and/or atmosphere-controlled chamber prior toultrasonic consolidation. The feedstock may be supported to minimizeslumping due to creep.

The feedstock may be T4, or may be aged, to T6, for example. Thefeedstock may be allowed to age naturally at room temperature, or a heatsource may be used to artificially age the consolidated feedstock. Thesubstrate may be aged or unaged. The source of the aluminum-basedfeedstock is in the form of tapes, sheets, wires, or droplets.

A system for depositing aluminum or an alloy thereof according to theinvention would include a source of aluminum-based feedstock, asubsystem for heat-treating the feedstock, and an ultrasonicconsolidation subsystem for bonding the heat-treated feedstock to asubstrate. Such apparatus may further include a temperature- and/oratmosphere-controlled chamber through which the feedstock passes priorto ultrasonic consolidation. A support may be provided to minimizeslumping due to creep. A heat source may be provided to artificially agethe consolidated feedstock. The subsystem for heat-treating thefeedstock may additionally perform a solution heat-treatment process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an automated ultrasonic consolidationsystem to which the invention is applicable;

FIG. 2 illustrates the use of support materials to fabricate an objectwith overhanging parts;

FIG. 3 a shows a stacking pattern for tape lay-up;

FIG. 3 b shows a basic feed arrangement for tape stock;

FIG. 3 c is a drawing of a horizontal section of the object showingadjacent tape segments;

FIG. 3 d is a drawing of a vertical section of the object showing thevertically stacked sections; and

FIG. 4 is directed to ultrasonically applying aluminum, in the form offoil, dots, or wires in a solution-heat-treated condition, over anexisting structure which might be in an aged or unaged condition.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic diagram of an automated ultrasonic consolidationsystem to which the invention is applicable. A computer-aided designunit 60 provides a layer-by-layer description of the object and of thesupport, as needed. The object material is fed onto the work area 75 byan object-material feed unit 64. The support material is fed onto thework area 75 by a support-material feed unit 62. The feed units may becombined into one when the shapes of the object and support layers arecompatible, for instance sheets of plastic are used for the support andsheets of aluminum foil for the object. In general, two different feedunits are required.

As shown in FIG. 2, the object may be fabricated by consolidatingsegments of tape 100 or filament or dots of material, as described belowin other embodiments of the invention, while the support for overhangingparts 95 of the object may be constructed by adding layers of supportmaterial 90.

The object layers may be either precut, or excess object may be removedby an object removing unit 80, which could be a mechanical or ultrasonicknife, drill, or milling tool, or a laser beam. If used, supportmaterial may be removed by a removing unit 85. Sporadic ultrasonicspot-welding of the support material may be limited to the extentnecessary to provide a rigid substrate for overhanging parts of theobject, thereby facilitating rapid removal of the support by cuttingthrough thin, unwelded sections of the support structure.

The CAD system 60 interfaces with a numerical controller 70, whichcontrols an actuation system (not shown). The actuation system bringsthe support feed unit 62, the support ultrasonic welding unit 66, theobject feed unit 64 and the object ultrasonic welding unit 68 intoproper position in the work area 75, so that the ultrasonicconsolidation of the layers takes place according to the CAD descriptionof the object and support. The actuation system also controls thevertical motion of the substrate or anvil and the motion of anyadditional vertical clamps required by the application, so that clampingpressure may be applied on two layers undergoing consolidation.

Feedstock in the form of sheets is often difficult to handle andmaintain under uniform in-plane tension and pressure orthogonal to itsplane; it may require very wide rollers to be fitted to the sonotrode,and successive passes of the roller to cover the entire sheet. Apreferred approach with respect to wide objects is to build such anobject from layers of material which are cut from a roll of tape. FIGS.3 a through 3 d illustrate the building of an object by tape lay-up.FIG. 3 a shows a typical lamination stacking pattern, in which thelayers of tape forming one section of the object have a direction whichis at a 90 degree angle with the direction of the layers of tape formingthe next section of the object.

The set-up of the operation is shown in FIG. 3 b. A feed spool 120 holdsthe tape 110, which passes through a tension roll 130 and is fed on tothe work area 75 to be consolidated with previous layers by the roller44 of a sonotrode. The tape is usually 1 to 2 inches wide. FIG. 3 c is adrawing of a horizontal section of the object showing adjacent tapesegments, and FIG. 3 d is a drawing of a vertical section of the objectshowing the vertically stacked sections.

For this process, ultrasonic vibrations are preferably transmitted intwo orthogonal directions, namely, between the horizontal sections, andbetween the vertical surfaces of adjacent segments of tape forming eachsection. Such a configuration permits full consolidation, so that thebond lines which are visible in the stacking pattern of FIG. 7 a, are nolonger visible after consolidation.

This invention more specifically resides in the deposition ofheat-treated aluminum using ultrasonic consolidation without disturbingthe properties of the underlying material(s). Aluminum is a lightweight,structural material that can be strengthened through alloying and,depending upon composition, further strengthened by heat treatmentand/or cold working. Among the advantages of aluminum are its lowdensity; a high strength-to-weight ratio; good resistance to corrosion;and ease of fabrication and diversity of form. Wrought and cast alloysare identified by a four-digit number, the first digit generallyidentifying the major alloying element used in the process. For castingalloys, the fourth digit is separate from the first three digits by adecimal point and indicates the form of the raw material.

The tempered designation appears as a hyphenated suffix to the basicalloy number. Four basic tempered designations are used for aluminumalloys. They are F for “fabricated”; O for “annealed”; H for“strain-harden” and T for “thermally treated.” There are many Tdesignations, including T4 which signifies solution heat-treated (SHT)and naturally aged to a substantially stable condition. This applies toproducts which are not cold worked after solution heat-treatment, or inwhich the affect of cold working flattened or straightening may not berecognized in mechanical property limits. T6, on the other hand,signifies solution heat-treated and then artificially aged. Mechanicalproperty limits are not affected by cold-working. Most alloys in the —Wand −T4 conditions are artificially aged to T6. There are manyvariations to both T4 and T6 treatments.

Referring to FIG. 4, the preferred embodiment of the invention isdirected to ultrasonically applying aluminum, in the form of foil 402,dots, or wires in a solution-heat-treated condition, over an existingstructure 404 which might be in an aged or unaged condition. Theultrasonically deposited SHT material is either allowed to age naturallyat room temperature, or a heat source of some kind, whether general orlocal, is applied to achieve an artificially aged condition such as T-6.The invention is applicable to any aging or non-aging aluminum alloysystem, or any other alloy system or alloy systems (since dissimilarmetals could be used). One or more of the alloys employed may bedeposited in a condition in which alloying elements are present in solidsolution and thermo-mechanical treatment can be used to increase thestrength of the material via precipitation hardening.

The build material may be generated in an SHT condition; for example, bysolution heat treating of the feed stock off-line, and maintaining itunder certain temperature conditions to prevent precipitation of solutesprior to ultrasonic consolidation of the SHT feedstock. Alternatively,the feedstock may be passed through a temperature- and/oratmosphere-controlled chamber 406 in an online process in which it isthen fed directly into an ultrasonic consolidation system 410.

The apparatus further preferably includes a mechanism 412 for supportingthe feedstock from slumping due to creep which may occur at the hightemperatures employed to solution heat treat aluminum alloys. Thefeedstock may be quenched via an argon quench or other atmospherecontrolled quenching technique to control feedstock surface condition asit is fed to the ultrasonic consolidation head, while maintaining thematerial in the SHT condition as it is cooled to the applicationtemperature and deposited. The system and method have numerous importantapplications, including aircraft and aerospace structures.

1. A method depositing aluminum or an alloy thereof, comprising thesteps of: heat treating an aluminum-based feedstock; and ultrasonicallyconsolidating the feedstack to a substrate.
 2. The method of claim 1,wherein the feedstock is solution heat treated.
 3. The method of claim1, wherein the feedstock is solution heat treated off line andmaintained under controlled temperature conditions to preventprecipitation of solutes prior to the ultrasonic consolidation.
 4. Themethod of claim 1, wherein the feedstock is heat-treated on-line bypassing it through a temperature- and/or atmosphere-controlled chamberprior to ultrasonic consolidation.
 5. The method of claim 1, wherein thefeedstock is supported to minimize slumping due to creep.
 6. The methodof claim 1, wherein the feedstock is T4.
 7. The method of claim 1,wherein the feedstock is aged.
 8. The method of claim 1, wherein thefeedstock is aged to T6.
 9. The method of claim 1, wherein the feedstockis allowed to age naturally at room temperature.
 10. The method of claim1, wherein a heat source is used to artificially age the consolidatedfeedstock.
 11. The method of claim 1, wherein the substrate is aged orunaged.
 12. The method of claim 1, wherein the substrate forms parts ofan aerospace or aircraft structure.
 13. A product constructed using theprocess of claim
 12. 14. A system for depositing aluminum or an alloythereof, comprising: a source of aluminum-based feedstock; a subsystemfor heat-treating the feedstock; and an ultrasonic consolidationsubsystem for bonding the heat-treated feedstock to a substrate.
 15. Thesystem of claim 14, wherein the feedstock is solution heat treated. 16.The system of claim 14, further including a temperature- and/oratmosphere-controlled chamber through which the feedstock passes priorto ultrasonic consolidation.
 17. The system of claim 14, furtherincluding a feedstock support to minimize slumping due to creep.
 18. Thesystem of claim 14, further including a heat source to artificially agethe consolidated feedstock.
 19. The system of claim 14, wherein thesubsystem for heat-treating the feedstock performs a solutionheat-treatment process.
 20. The system of claim 14, wherein the sourceof aluminum-based feedstock is in the form of tapes, sheets, wires, ordroplets.